Saturated aldehyde series

In this article we examine results obtained in a direct quantum calculation (based on the semiempirical MINDO/3 method) of the electrooptical parameters (EOPs) and the optimized molecular geometry of a series of saturated aldehydes: formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and valeraldehyde. The quantum calculation was performed in a system of dependent natural coordinates. The EOPs of the molecules were found within the framework of a valence—optical scheme and have been used in solving problems of determining intensities of IR absorption bands. Theoretical and experimental curves have been compared.K. A. Timiryazev Agricultural Academy. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 157–168, January–February, 1993.     

Influence of pore dimension and sorption configuration on the heat of sorption of hexane on monodimensional siliceous zeolites

Sorption of n-hexane on monodimensional pure silica SSZ-35, CIT-5, ZSM-12, and ZSM-22 zeolites with different pore dimension and on recently synthesized ITQ-29 was studied by IR spectroscopic and computational chemistry methods. Heats of sorption of n-hexane on these zeolites was determined experimentally from the temperature dependence of the intensity of IR bands of sorbed hexane as well as from theoretical calculations. Calculations have shown the different orientations of sorbed hexane molecules inside zeolite channels, which depend on the type of zeolite and loading. At high loadings, ordering of hexane inside the channels is observed due to optimization of sorbate-sorbate and sorbate-zeolite interaction energies. Such ordering is responsible for the increase of the sorption energy. A decrease of the sorption energy upon increasing the pore dimension of zeolite was observed, in agreement with results previously published in the literature. Effects of pore diameter of zeolites and ordering of molecules inside zeolite channels on the sorption energy of hexane are discussed.     

On the theory of processes in reaction centers of polyatomic molecules

Based on general principles of quantum theory of chemical transformations for polyatomic molecules, the notion of the reaction center (RC) was revised. The presence of RCs is a necessary condition for occurrence of all types of chemical transformations in complex systems. The physical picture of processes in RCs, conditions for maximum probability of transformations, the local character of a chemical reaction and its relation to the characteristic vibrations, and the methods of a priori search for RCs based on normal coordinate analysis of coupled states and on calculations of overlap integrals between vibrational wave functions were studied. Specific features of manifestation of characteristic vibrations in vibrational and vibronic spectra were investigated and the possibility of search for RCs using optical spectroscopy was considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1267–1273, August, 2006.     

A possible mechanism of image recognition by molecules and the design of receiving-and-transforming systems

The problem of the mechanism of image recognition by a complex molecular system based on a set of independent primary signals is considered. Image recognition is interpreted as the appearance of a structural transformation in one remote receiving-and-recording center taking place when and only when all the primary signals have appeared. This principle ensures the most economical pattern for the information and energy transfer. The necessary properties of the receiving-and-transforming molecular elements are discussed. The task of designing a receiving-and-transforming molecular system is reduced to solution of either a formal logical equation or a set of kinetic differential equations of a special form. Examples of computer simulations are given.     

On Feasibility of “Spectroscopic” Calculations of XH Bond Dissociation Energies for Polyatomic Molecules from Fundamental Vibration Frequencies Using the Anharmonic Molecular Model

This paper discusses the applicability of the variational technique using a minimal Morse-harmonic basis set to calculations of the fundamental spectrum and the potential function parameters for polyatomic molecules. The potential function is assumed to be the sum of the Morse function for XH bonds and the harmonic function for the skeletal and deformation vibrations. The initial approximation for the potential function is found by ab initio calculations and refined by solving the inverse mechanical problem (selecting the scaling indices). The thus selected harmonic part of the potential function gives equally good agreement between the experimental and calculated transition frequencies in both harmonic and anharmonic approximations. The anharmonic (Morse) term of the potential function (bond dissociation energy) is selected by solving the inverse mechanical problem until the best agreement between the experimental and calculated CH bond stretching frequencies has been achieved. Problem solving ends with the construction of a transmission curve in the IR spectrum. Variations of the dipole moment of the molecule induced by vibrations are found by ab initio calculations.     

Effect of the components of the raman scattering tensor on band intensities

The Raman scattering (RS) tensor as a function of excitation radiation frequency is studied taking into account, the vibration quantum. It is shown that the corresponding asymmetric components of the tensor are described by fast converging series. Expressions are obtained for the antisymmetric and symmetric components of the RS tensor. A convenient formula is proposed for the calculation of the RS tensor and its components, where the tensor is represented as a sum of the derivative of static polarizability and the terms containing fast converging series. The formula makes it possible to avoid infinite summation. Computer experiments simulating the dependence of the intensity of RS bands and their components on the excitation frequency are carried out. Moscow State University of Building Engineering. V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 6, pp. 1006–1015, November–December, 1996. Translated by I. Izvekova     

Composition and experience in operation of library of molecular structures as software for large-scale calculations of infrared spectra of organic compounds

In this article we describe the composition of a library of molecular structures and evaluate its capabilities for modeling IR spectra of complicated compounds. A predictive calculation of an IR spectrum is performed for the molecule of 1-phenyl-4-(p-tolyl)-1,3-butadiene on the basis of the library of molecular structures, and the theoretical and experimental spectra of this molecule are compared.K. A. Timiryazev Agricultural Academy. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 197–201, January–February, 1993.